I first saw that episode as a kid in the mid-70's, when TOS had just gone into syndication.. It was and still is one of my favorites. The two best lines in the episode are "He knows Doctor, He knows..." that Spock said right after her demise as Kirk held back McCoy from saving her. And then Kirk's closing line "Let's get the hell out of here." A pretty intense line for 1960's TV, and no happy ending.